The assembly process for various industrial products such as automobiles is becoming more and more automated in order to improve efficiency and quality. While some assembly processes, such as welding, painting, etc. can be fully automated; there remain a number of processes that require a significant amount of operator involvement. In particular, joining two or more parts together with threaded fasteners such as bolts, nuts, screws, etc. often requires an operator to manipulate a hand-held tool to perform the operation.
Air tools are commonly used to apply torque to threaded fasteners when joining two or more parts together. Nut runner air tools, for example, are used to provide relative rotation between a nut and bolt by running the nut along the bolt to form a fastener joint connection. The torque applied is substantially increased under load as the fastener connection approaches completion. In order to apply a specified torque, torque shut off valves have been used in air tools to shut off the air supply to the tool motor when a desired torque specification is achieved.
The critical nature of certain fastener joints requires careful control of when threaded fasteners are tightened. Insufficient torque can result in fastener joints becoming loose and failing. Excessive torque can damage threaded fasteners or create excessive stain that can result in fastener joint failure. Different size threaded fasteners generally have different torque requirements when used to form fastener joints, with the amount of torque typically increasing with the size of the threaded fasteners.
There are a number of torque control systems as exemplified by U.S. Pat. No. 5,713,250 to Hendricks et al., U.S. Pat. No. 5,377,578 to Borries, U.S. Pat. No. 5,177,919 to Borries et al., U.S. Pat. No. 5,229,931 to Takeshima et al., U.S. Pat. No. 5,014,794 to Hansson, U.S. Pat. No. 6,390,205 to Wallgren et al., and U.S. Pat. No. 6,055,484 to Lysaght.
Of these patents, U.S. Pat. No. 5,713,250 to Hendricks et al. discloses a system that includes a socket tray 78 that holds four different size sockets 92 in socket holders 200. At the bottom of each socket holder 200 is a conventional, normally closed, single pole, push button activated switch 202. When a socket 92 is removed from one of the socket holders 200 the associated push button switch sends a signal to the trigger switch box 73 which in turn sends a signal to controller 72 which controls the torque applied by tightening wrench (nut runner) 75.
In addition to U.S. Pat. No. 5,713,250 to Hendricks et al., U.S. Pat. No. 5,405,025 to Melrose discloses a socket tray that includes sensing switches or microswitches 20 that are positioned along the respective socket centerline positions and switch activators 21 that contact sockets when they are disposed within the socket tray.
Even though the use of mechanical contact switches in socket trays is conventional, they generally have a high or frequent failure rate. This is because, in order to operate, the mechanical contact switches have to be contacted with sockets as the sockets are placed in the socket tray. During actual use, operators typically slam the sockets into the socket trays which results in shock and impact damage to the mechanical contact switches and eventual failure.
The present invention provides a socket tray for torque control systems that is designed and configured to avoid the use of mechanical switches that require contact activation and the problems associated therewith.